A significant advancement with respect to gauges for determining the liquid level within a boiler was the bi-color principle disclosed in the Blackburn U.S. Pat. Nos. 2,024,815 and 2,115,899. The basis for this principle is that steam and water have different indices of refraction. By directing light from differently colored light sources, such as red and green light sources, through a specially formed prismatic gauge tube assembly, the portion of the gauge tube containing steam appears red in color to the observer while the portion of the gauge tube containing water appears green in color. Because of these different colors, this type of gauge makes it possible to easily detect whether the gauge glass is full or empty and minimizes the possibility that the observer might mistake a gauge full of water for a gauge full of steam which could lead to disastrous results.
Variations of the bi-color principle disclosed in the foregoing Blackburn patents have been developed and incorporated into other liquid level gauges in order to minimize the possibility of human error with respect to determining the presence and/or the level of steam or water in a gauge glass. These modifications have minimized the possibility of such human error when viewing the gauge but have not eliminated the possibility of an erroneous reading.
Because of the foregoing, it has become desirable to develop a system which eliminates the possibility of human error when determining the level of steam and/or water in a boiler installation.